This invention relates to a token train retrieval device for retrieving tokens including multi-media information which is communicated between heterogeneous data processing systems.
The token train retrieval device is for use in processing of protocol conversion between the heterogeneous data processing systems, processing of protocol analysis therebetween, hypertext search, retrieval of a multi-media data base, or the like. The token train retrieval device is necessary to communication and retrieval of the multi-media information between the heterogeneous data processing systems which are connected to one another in an information communication network. The information communication network is built on the basis of a network architecture systematized according to a protocol.
Inasmuch as such a protocol has been originally developed by each of computer makers, it is impossible to carry out information interchange between the heterogeneous data processing systems. In order to solve this problem, a standard protocol has been established by the International Organization for Standardization (ISO). This standard protocol is called a layer protocol of Open System Interconnection (OSI) in the art. Such a layer protocol is disclosed in a book written by William Stallings and published 1985 by Macmillan Publishing Company, New York, under the title of "DATA AND COMPUTER COMMUNICATIONS", pages 394 to 408, Chapter 12.
The layer protocol consists of seven layers which comprises a physical layer, a data link layer, a network layer, a transport layer, a session layer, a presentation layer, and an application layer. Each layer of the layer protocol has a processing function which should be standardized between the computer makers. Inasmuch as the layer protocol of the OSI is well-defined, it is possible to carry out protocol conversion between the layer protocol and a specific protocol developed by a particular computer maker. Each of the heterogeneous data processing systems comprises a protocol conversion system which carries out the protocol conversion. By the protocol conversion, it is possible to carry out the information interchange between the heterogeneous data processing systems.
Attention will be directed to the application layer. As is known in the art, the application layer is divisible into first through N-th sublayers where N represents a predetermined natural number which is equal to, for example, sixty-four. The first through the N-th sublayers are referred to as first through N-th nest levels, respectively, in the art. The first through the N-th nest levels are a lowest through a highest nest level, respectively. According to the application layer, data transmission is carried out between the heterogeneous data processing systems on the basis of Message Handling Systems (MHS) recommended by the International Telegraph and Telephone Consultive Committee (CCITT) Recommendation X.409.
More specifically, the multi-media information is transmitted between the heterogeneous data processing systems as a plurality of tokens. Each of the tokens is given by a nest level selected from the first through the N-th nest levels as a selected level. Each of the tokens comprises a header and a data set as described in Chapter 12 of the above-mentioned book. The data set has a data length and is for nesting one of the tokens that has a higher nest level than the selected level and will be referred to as a particular token. The header comprises a data length code representative of the data length and a data identifier code. The data identifier code includes a nest bit indicative of whether or not the particular token is nested in the data set.
In a conventional token train retrieval device, the tokens are memorized in a memory device as stored tokens. Each of the stored tokens starts at a starting address and ends at an end address. In prior art, retrieval of a specific token selected from the stored tokens is carried out after the stored tokens are successively read from the memory device as read tokens and the header of each of the read tokens is decoded. The specific, token has a designated nest level and the header includes a designated identifier code. Both of the designated nest level and the designated identifier code are given as a retrieval condition. More specifically, a nest level of each read token is decided by decoding the header of each read token as the selected level. Subsequently, a check is made between the selected level and the designated nest level. After decision of the selected level, the retrieval of the specific token is performed by software in a computer. The conventional token train retrieval device has been therefore disadvantageous in that a long processing time is consumed to locate the specific token which satisfies the retrieval condition. As a result, it is impossible to rapidly and smoothly carry out selection of the specific token and processing of the protocol conversion.